This invention relates generally to equipment for testing material properties, and more specifically relates to hardness testers used to determine the hardness of a material.
Penetration hardness testers are well-known in the art. These hardness testers generally include an indentor tip that is driven to apply a load to the test specimen. Some hardness testers known as deadweight testers utilize gravity acting on weights to create the force which drives the indentor into the test specimen. Other hardness testers utilize an electric motor to drive the indentor. In either case, the force or load on the indentor relative to the depth of penetration of the indentor into the surface of the specimen, or relative to the diameter of the indentation, will give a hardness number measured on a common scale such as Rockwell or Brinell.
Inaccuracies in testing arise due to many sources, such as relative movement between mechanical components. Recent improvements to such hardness testers have come by the use of various electronic equipment, such as load cells to measure the applied force and displacement sensors to measure the depth of penetration. Closed-loop systems utilizing a central processor or computer, especially in conjunction with load cells and displacement transducers, have provided improved reliability to hardness testers. Despite these advances, there remains a need to provide a hardness tester with improved accuracy.
Further, known hardness testers utilize a vertically adjustable anvil to properly position the test specimen at a discrete position for testing. However, not all specimens may easily be positioned on the anvil for testing. Hence, there exists a need to provide a hardness tester that is adaptable for different specimens, including for a variety of situations.
The invention provides a hardness tester which not only obtains improved accuracy, but also is adaptable to a variety of situations and specimens. These and other advantages of the invention, as well as additional inventive features, will be apparent from the description of the invention provided herein when taken in conjunction with the accompanying drawings.
One embodiment of he present invention provides a hardness tester for determining the hardness of a specimen. The hardness tester generally comprises a tester assembly is supported on a frame assembly. The tester assembly has a tester housing that supports a motor drivingly connected to a load cell and an indentor. The frame assembly includes a vertically oriented plate having a general C-shape defined by upper and lower arms connected by a main body. The plate is fabricated from a unitary sheet of metal to provide rigidity in the vertical direction.
According to more detailed features of the embodiment, by virtue of the C-shaped plate, the upper and lower arms deflect less than 0.0015 inches apart in response to a separating force of 330 lbs. The lower arm supports an anvil for supporting the specimen. It is also preferable to provide a second vertically oriented plate having a general C-shape, the second plate being laterally spaced from the first plate to define side walls of the frame. Here, the free ends of the upper arms are connected by a mounting plate having a mounting surface engaging the tester housing.
In another embodiment of the present invention, a hardness tester is provided that generally comprises a frame assembly and a tester assembly. The frame assembly includes an upper arm and a lower arm, and the tester assembly includes a tester housing supporting a motor drivingly connected to a load cell and an indentor. The tester assembly is selectively attachable to the frame assembly at a frame mounting surface defined by the upper arm of the frame assembly.
According to more detailed features of this embodiment, the tester assembly includes a tester mounting surface for engaging the frame mounting surface. Preferably, the tester mounting surface and frame mounting surface are keyed together. It is also preferable that the tester mounting surface and the frame mounting surface extend at least 4 inches in the vertical direction. The tester mounting surface and frame mounting surface each include a plurality of corresponding mounting holes for selectively attaching the tester and frame assemblies, typically by threaded fasteners.
In yet another embodiment of the present invention, a hardness tester is provided that generally comprises a tester housing supporting a motor operatively connected to a ball screw assembly. The ball screw assembly is connected to the tester housing and includes a ball screw, a ball spline, and a ball spline bearing. The ball screw is operatively connected to the motor. The ball spline has a hollow center for receiving the ball screw, and includes a ball nut securely attached thereto. A downward end of the ball spline is directly connected to a load cell and an indentor. The ball spline bearing is attached to the housing and receives the ball spline to prevent rotation of the ball spline. The ball nut threadingly engages the ball screw for transforming the rotational movement of the ball screw into linear movement of the ball spline and indentor.
According to more detailed aspects of this embodiment, the ball spline includes a plurality of circumferentially spaced grooves extending along the length of the ball spline, the spine bearing engaging each groove to prevent rotation of the ball spline and guide linear movement. Preferably, a displacement sensor is provided that has a read head and a tape scale; the tape scale being attached to the outer periphery of the ball spline and the read head being attached to the tester housing and positioned to read the tape scale. A CPU is operatively connected to the motor, displacement sensor, and load cell to control the movement of the ball spline and indentor to perform hardness tests. Preferably, first and second limit switches are connected to the tester housing, the first and second limit switches being vertically spaced to define an operating range for the ball spline and indentor.